Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
  • G01N23/02—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material
  • G01N23/04—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and forming images of the material
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
  • A61B6/42—Arrangements for detecting radiation specially adapted for radiation diagnosis
  • A61B6/4208—Arrangements for detecting radiation specially adapted for radiation diagnosis characterised by using a particular type of detector
  • A61B6/4216—Arrangements for detecting radiation specially adapted for radiation diagnosis characterised by using a particular type of detector using storage phosphor screens
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
  • A61B6/50—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment specially adapted for specific body parts; specially adapted for specific clinical applications
  • A61B6/502—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment specially adapted for specific body parts; specially adapted for specific clinical applications for diagnosis of breast, i.e. mammography
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
  • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
  • G01T1/16—Measuring radiation intensity
  • G01T1/20—Measuring radiation intensity with scintillation detectors
  • G01T1/2012—Measuring radiation intensity with scintillation detectors using stimulable phosphors, e.g. stimulable phosphor sheets
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
  • G03B42/00—Obtaining records using waves other than optical waves; Visualisation of such records by using optical means
  • G03B42/02—Obtaining records using waves other than optical waves; Visualisation of such records by using optical means using X-rays
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
  • G03B42/00—Obtaining records using waves other than optical waves; Visualisation of such records by using optical means
  • G03B42/02—Obtaining records using waves other than optical waves; Visualisation of such records by using optical means using X-rays
  • G03B42/028—Industrial applications

Definitions

• the present invention relates to a method for recording and reproducing images of objects made by high energy radiation. It relates especially to a method for manufacturing a cesium halide storage phosphor, particular phosphors and a storage phosphor panel containing them.
• a well-known use of phosphors is in the production of X-ray images.
• an X-ray radiograph is obtained by X-rays transmitted image-wise through an object and converted into light of corresponding intensity in a so-called intensifying screen (X-ray conversion screen) wherein phosphor particles absorb the transmitted X-rays and convert them into visible light and/or ultraviolet radiation to which a photographic film is more sensitive than to the direct impact of X-rays.
• a special type of phosphor is used, known as a photostimulable phosphor, which being incorporated in a panel, is exposed to incident pattern- wise modulated X-ray beam and as a result thereof temporarily stores energy contained in the X-ray radiation pattern.
• a beam of visible or infra-red light scans the panel to stimulate the release of stored energy as light that is detected and converted to sequential electrical signals which are can be processed to produce a visible image.
• the phosphor should store as much as possible of the incident X-ray energy and emit as little as possible of the stored energy until stimulated by the scanning beam. This is called “digital radiography” or “computed radiography”.
• digital radiography or “computed radiography”.
• the image quality that is produced by a conventional as well as by a digital radiographic system depends largely on the construction of the phosphor screen. Generally, the thinner a phosphor screen at a given amount of absorption of X-rays, the better the image quality will be. This means that the lower the ratio of binder to phosphor of a phosphor screen, the better the image quality, attainable with that screen, will be. Optimum sharpness can thus be obtained when screens without any binder are used.
• Such screens can.be produced, e.g., by physical vapor deposition, which may be thermal vapor deposition, sputtering, electron beam deposition or other of phosphor material on a substrate.
• physical vapor deposition which may be thermal vapor deposition, sputtering, electron beam deposition or other of phosphor material on a substrate.
• this production method can not be used to produce high quality screens with every arbitrary phosphor available.
• the mentioned production method leads to the best results when phosphor crystals with high crystal symmetry and simple chemical composition are used.
• Phosphors having complicated crystal structures as, e.g., alkaline earth fluorohalides, tend to decompose (partially) under physical vapor deposition and the production of screens in this way while using phosphors with complicated crystal structure is quasi impossible and leads to sub-optimal results.
• alkali metal halide phosphors in storage screens or panels is well known in the art of storage phosphor radiology and the high crystal symmetry of these phosphors makes it possible to provide structured screens and binderless screens.
• U.S. Patent No. 5,055,681 a storage phosphor screen comprising an alkali metal phosphor in a pile-like structure is disclosed.
• U.S. Patent No. 5,736,069 an alkali metal storage phosphor is disclosed corresponding to the formula : Ml + X.aM2+X'2_bM3 + X"3:cZ wherein: M ⁇ + is at least one member selected from the group consisting of Li, Na, K,
• M2+ is at least one member selected from the group consisting of Be, Mg, Ca, Sr, Ba, Zn, Cd, Cu, Pb and Ni,
• M3+ is at least one member selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Bi, In and Ga,
• Z is at least one member selected from the group Gal + , Ge2+, Sn2+, Sb3 + and As3 + , X, X' and X" can be the same or different and each represents a halogen atom selected from the group consisting of F, Br, Cl, and I, and 0 ⁇ a ⁇ l, 0 ⁇ b ⁇ l and 0 ⁇ c ⁇ 0.2.
• alkali metal phosphors according to the disclosures mentioned above find applications for preparing structured screens and binderless screens, it would, nonetheless, be advantageous to have CsX phosphor with enhanced speed.
• the object of the invention is realized by providing a method for manufacturing a CsX:Eu stimulable phosphor, wherein X represents a halide selected from the group consisting of Br, Cl and combinations thereof comprising the steps of:
• CsX with between 10 ⁇ 3 mol % and 5 mol % of a Europium compound, relative to the moles of CsX, the Europium compound being selected from the group consisting of EuX'2, EuX'3 and EuOX', X' being one or more halide selected from the group consisting of F, Cl, Br and I;
• the resulting CsX:Eu phosphor is recovered from the crucible or other suitable container in which it was prepared.
• the CsX:Eu phosphor resulting from such methods is novel, and provides substantial practical advantages over known CsX:Eu phosphors.
• the second object of the invention is realized by manufacturing a phosphor screen containing a CsX:Eu stimulable phosphor, wherein X represents a halide selected from the group consisting of Br, Cl and combinations thereof comprising the steps of:
• phosphor on a substrate by a method selected from the group consisting of chemical vapor deposition or physical vapor deposition, including thermal vapor deposition, electron beam evaporation, magnetron sputtering, radio frequency sputtering and pulsed laser deposition or atomization techniques such as spray drying, thermal spraying, etc.
• chemical vapor deposition or physical vapor deposition including thermal vapor deposition, electron beam evaporation, magnetron sputtering, radio frequency sputtering and pulsed laser deposition or atomization techniques such as spray drying, thermal spraying, etc.
• the second object of the invention is also realized by manufacturing a phosphor screen containing a CsX:Eu stimulable phosphor, wherein X represents a halide selected from the group consisting of Br, Cl and combinations thereof comprising the steps of:
• the third object of the invention is realized by providing a method for recording and reproducing images of objects made by high energy radiation comprising the steps of: - exposing a panel containing a CsX:Eu stimulable phosphor, wherein X represents a halide selected from the group consisting of Br, Cl and combinations thereof, including between 10 ⁇ 3 mol % and 5 mol% of a Europium dopant, said dopant originating from a Europium compound selected from the group consisting of EuX'2, EuX'3 and EuOX', X' being one or more halide selected from the group consisting of F, Cl, Br and I, with X-ray radiation for storing energy in said phosphor,
• Fig. 1 shows the emission spectrum of an invention CsB ⁇ Eu phosphor.
• Fig. 2 shows the stimulation spectrum of an invention CsBr:Eu phosphor.
• Fig. 3 shows the conversion efficiency of the CsBr:Eu phosphors as a function of the concentration and the type of dopant.
• Fig. 4 shows the ultra-violet excited (280 nm) luminescence spectrum recorded from a film of europium doped cesium bromide.
• X-ray has to be understood as any penetrating radiation and includes irradiation originating from a radioisotope (e.g. C06O, Irl92, Se75, etc.), radiation created by an X-ray generator of any type, radiation and high energy particles created by a high energy radiation generator (e.g. Betatron), and/or radiation from a sample labeled with a radioisotope as is the case of, e.g., autoradiography.
• a radioisotope e.g. C06O, Irl92, Se75, etc.
• a high energy radiation generator e.g. Betatron
• EP-A-174 875 there is no teaching that in the manufacturing of alkali metal halide phosphors the use of different Europium compounds for doping the alkali metal halide would give phosphors with different quality or enhanced qualities (e.g., enhanced properties).
• EU2O3 is a suitable compound for doping a simple CsBr phosphor.
• the CsX:Eu phosphor of the present invention is prepared by using as an Eu dopant in the raw mix a Europium compound selected from the group consisting of EuX'2, EuX'3 and EuOX', where X' is one or more halide selected from the group consisting of F, Cl, Br and I.
• a Europium compound selected from the group consisting of EuX'2, EuX'3 and EuOX', where X' is one or more halide selected from the group consisting of F, Cl, Br and I.
• EuBr 3 , EuBr 2 , EuCl 2 and EuOBr gave very good results. This result was even more surprising when consideration is given to the observation that when doping a CsBr phosphor with Tl, better performance was achieved using TI2O instead of TlBr.
• the Europium compound selected from the group consisting of EuX'2, EuX'3 and EuOX', X' being one or more halide selected from the group consisting of F, Cl, Br and I, is preferably mixed with the CsX in such a way that between 10 ⁇ 3 mol % and 5 mol % of the Europium compound is present, relative to the number of moles of CsX.
• X' being one or more halide selected from the group consisting of F, Cl, Br and I
• Europium compound is mixed with the CsX in such a way that between 10 ⁇ 1 mol % and 3 mol % of the Europium compound is present relative to the CsX. These starting materials are combined and/or intimately mixed by suitable methods known in the art.
• the combined starting materials are preferably heated (e.g., fired) at a temperature ranging from about 450°C to about 1000°C, more preferably at a temperature ranging from about 550°C to about 1000°C, and still more preferably at a temperature ranging from about 650°C to about 1000°C and most preferably at a temperature of about 700°C.
• the dwell time at the firing temperature is not critical, and can range from about 1 minute to about 10 hours, from about 5 minutes to about 6 hours or from about 5 minutes to about 1 hour.
• the combined starting materials are most preferably heated to a temperature (e.g., fired at temperatures) above the melting point of CsBr.
• the heated mixture can be cooled by methods known in the art. Cooling rates can be typical of those employed in the art and can vary based on the method of cooling.
• the phosphors of the present invention include a mixture of halides in the formula CsX:Eu, where X is a mixture of Br and Cl.
• a ranges from about 0.99 to about 0.95 and b ranges from about 0.01 to about 0.05.
• a may range from about 0.95 to about 0.8 or from about 0.9 to about 0.8; also, b may range from about 0.05 to about 0.2 or from about 0.1 to about 0.2.
• These phosphors may be prepared by the vapor deposition methods discussed herein by starting with targets of CsBr, CsCl and EuCl 2 and controlling the deposition.
• the phosphors prepared by the aforementioned methods exhibit substantially improved speed. Moreover, all samples of CsBr:Eu prepared with europium halides in the raw mixtures exhibited a blue photoluminescence (254 nm excitation) after firing with a power in Watt that is at least 100 times higher than the energy of a very weak red photoluminescence. Samples prepared with Eu 2 O 3 as the starting material exhibited blue and red photoluminescence (254 nm excitation) after firing, wherein the power of the blue photoluminescence is substantially less than 100 times the energy of the red photoluminescence.
• the phosphor produced by the methods described herein can beneficially be used in a powder panel wherein the phosphor is applied to a support from a solution containing a binder resin and the phosphor.
• Phosphor screens comprising a layer containing a phosphor embedded in a binder resin are well known in the art. In this case any binder known in the art can be used to form a screen or panel comprising a CsB ⁇ Eu or CsBr a Cl b :Eu phosphor according to the present invention.
• Suitable binders are, e.g., gelatin, polysaccharides such as dextrin, gum Arabic, and synthetic polymers such as polyvinyl butyl, polyvinyl acetate, nitrocellulose, ethylcellulose, vinylidene chloride-vinyl chloride copolymer, polyalkyl (meth)acrylate, vinyl chloride-vinyl acetate copolymer, polyurethane, cellulose acetate, cellulose acetate butyrate, polyvinyl alcohol, polystyrene, polyester, etc.
• synthetic polymers such as polyvinyl butyl, polyvinyl acetate, nitrocellulose, ethylcellulose, vinylidene chloride-vinyl chloride copolymer, polyalkyl (meth)acrylate, vinyl chloride-vinyl acetate copolymer, polyurethane, cellulose acetate, cellulose acetate butyrate, polyvinyl alcohol, polystyrene,
• a mixture of two or more of these binders may be used, e.g., a mixture of polyethyl acrylate and cellulose acetobutyrate.
• the weight ratio of phosphor to binder is generally within the range of from 50:50 to 99:1, preferably from 80:20 to 99:1.
• a self-supporting or supported layer of phosphor particles according to the present invention comprises said particles dispersed in a binding medium and a protective coating thereover characterized in that the binding medium substantially consists of one or more hydrogenated styrene-diene block copolymers, having a saturated rubber block, as rubbery and/or elastomeric polymers.
• the polymer can be represented by the formula A-B-A (tri-block) or by the formula A-B (di-block), wherein A represents styrene and B represents the hydrogenated diene block, e.g., ethylene-butylene or ethyl ene-propylene. Further the ratio by volume of phosphor to binding medium is preferably more than 70/30 and still more preferably more than 85/15.
• the phosphor is especially well suited for manufacturing a "binderless" storage phosphor panel by physical vapor deposition comprising the deposition so as to have a "binderless” phosphor screen.
• any method for depositing a phosphor without a binder can be used to apply the cesium halide phosphor made by the method of this invention (e.g., CsX:Eu or CsBr a Cl t ,:Eu) to a support
• thermal vapor deposition is used to prepare binderless screens containing a phosphor of this invention.
• the deposition of the phosphor according to this invention is preferably so that the CsX:Eu stimulable phosphor is present in the form of columnar crystals.
• Such panels have been disclosed in, e.g., EP-A-185 534, U.S. Patent No. 4,947,046, JP-A-61 245099, etc.
• this phosphor is brought in to a heatable vessel. This vessel and the substrate are brought in a deposition chamber that can be evacuated to at least
• the thickness of the phosphor layer on the substrate can be adjusted.
• a "binderless" storage phosphor panel containing a cesium halide phosphor can also be manufactured depositing simultaneously CsX and EuX'2, EuX'3 and/or EuOX', X being a combination of Br and Cl in any ratio and X' being one or more halides.
• the invention encompasses a method for manufacturing a phosphor screen containing a CsX:Eu stimulable phosphor, wherein X represents a halide selected from the group consisting of Br and Cl comprising the steps of:
• the deposition can proceed from a single container containing a mixture of the starting compounds in the desired proportions.
• the method encompasses further a method for manufacturing a phosphor screen containing a CsX:Eu stimulable phosphor, wherein X represents one or more halides selected from the group consisting of Br and Cl comprising the steps of:
• - depositing said mixture on a substrate by a method selected from the group consisting of chemical vapor deposition or physical vapor deposition, including thermal vapor deposition, electron beam evaporation, magnetron sputtering, radio frequency sputtering and pulsed laser deposition or atomization techniques such as spray drying, thermal spraying, etc.
• chemical vapor deposition or physical vapor deposition including thermal vapor deposition, electron beam evaporation, magnetron sputtering, radio frequency sputtering and pulsed laser deposition or atomization techniques such as spray drying, thermal spraying, etc.
• Bringing in condition for thermal vapor deposition means that the ingredients are brought in heatable containers and that these containers are placed, together with the substrate on which the phosphor has to be deposited in a deposition chamber that can be evacuated to at least 10 ⁇ 4 mbar.
• the starting ingredients are mixed into a single heatable container, the starting ingredients are separated into individual heatable containers and the pre-formed CsX:Eu phosphor is placed into one or more heatable containers.
• Support materials for storage screens, binderless as well as binder containing screens, containing a phosphor in accordance with the present invention include cardboard, plastic films such as films of cellulose acetate, polyvinyl chloride, polyvinyl acetate, polyacrylonitrile, polystyrene, polyester, polyethylene terephthalate, polyamide, polyimide, cellulose triacetate and polycarbonate; metal sheets such as aluminum foil and aluminum alloy foil; ordinary papers; baryta paper; resin-coated papers; pigment papers containing titanium dioxide or the like; papers sized with polyvinyl alcohol or the like; and glass sheets.
• plastic films such as films of cellulose acetate, polyvinyl chloride, polyvinyl acetate, polyacrylonitrile, polystyrene, polyester, polyethylene terephthalate, polyamide, polyimide, cellulose triacetate and polycarbonate
• metal sheets such as aluminum foil and aluminum alloy foil
• ordinary papers baryta paper
• resin-coated papers pigment papers
• a plastic film is preferably employed as the support material for a binder containing screen; a glass or Al sheet is preferably employed as the support material for a binderless screen.
• the plastic film may contain a light-absorbing material such as carbon black, or may contain a light-reflecting material such as titanium dioxide or barium sulfate.
• the former is appropriate for preparing a high-resolution type storage screen, while the latter is appropriate for preparing a high-sensitivity type storage screen.
• Examples of preferred supports include polyethylene terephthalate, clear or blue colored or black colored (e.g., LUMIRROR C, type X30, (trade name) supplied by Toray
• polyethylene terephthalate filled with TiO 2 or with BaSO polyethylene terephthalate filled with TiO 2 or with BaSO .
• Metals such as e.g. aluminum, bismuth and the like may be deposited e.g. by vaporization techniques to get a polyester support having radiation-reflective properties.
• These supports may have a thickness which may differ depending on the material of the support, and may generally be between 60 and 1000 mm, more preferably between 80 and 500 mm from the standpoint of handling.
• the "prompt" emission spectrum of the phosphor under X-ray excitation was measured.
• the measurement proceeds with a multichannel detector under excitation by X-ray irradiation and was carried out with an X-ray source operating at room temperature at 80 kVp and 15 mA. Under continuous X-ray excitation light of different wavelengths were produced. The rays of emission light, having different wavelengths, were collected and amplified in the different channels of the multichannel detector.
• the stimulation spectrum was determined.
• the light of a tungsten (quartz-iodine) lamp was fed into a monochromator (SPEX 270M trade name of Yvon-Jobin, France) and then mechanically chopped with a rotating wheel with a single slit.
• the lamp provides a continuous spectrum extending from the near UV through the visible spectrum into the infrared.
• the 520.24.33.0 grating from Yvon-Jobin was a 1200 line/mm grating covering the visible range from 350 nm to 1100 nm in the first order and was blazed at 750 nm.
• the wavelength of the stimulating light can be set via a step motor connected to the monochromator under the control of a computer.
• the second harmonic of the monochromator was eliminated by placing a 4 mm Schott GG435 filter in front of the phosphor screen, when the monochromator is set at a wavelength longer than 800 nm a RG 665 SCHOTT filter (trade name) was added.
• any residual energy still present in the phosphor screen was removed by irradiation with light of a 500 W quartz-halogen lamp.
• the phosphor screen was then excited with an X-ray source operating at 80 kVp and 5 mA.
• an X-ray source operating at 80 kVp and 5 mA.
• the BALTEAUGRAPHE 2000 (tradename) X-ray source of Balteau, France was used.
• the low energy X-rays are filtered out with a 21 mm thick aluminum plate to harden the X-ray spectrum.
• the phosphor screen was transferred in the dark to the measurement set-up. In this setup laser light was used to photostimulate the X-ray irradiated phosphor screen.
• the laser used in this measurement was a diode laser emitting at 690 nm with a power of 5 mW.
• the diode laser was the type LT030-MD, trade name of Sharp, USA.
• the laser-optics comprise an electronic shutter, a beam-expander and a filter.
• a photomultiplier (HAMAMATSU R 376) collects the light emitted by the photostimulation and gives a corresponding electrical current.
• the measurement procedure was controlled by a Hewlett Packard HP 382 (tradename) computer connected to a HP 6944 (tradename) multiprogrammer. After amplification with a current to voltage converter a TEKTRONIX TDS 420 (tradename) digital oscilloscope visualizes the photocurrent obtained.
• the laser beam begins to stimulate the phosphor screen and the digital oscilloscope was triggered.
• the light 2 emitted by only 7 mm was collected. Approximately half of the laser power (2 mW) reaches the screen surface. In this way the intensity of the stimulating beam was more uniform.
• the stimulating laser light (transmitted by the crystal) and the stimulated emission light are separated by a 6 mm BG 39 SCHOTT (trade name) filter, so that only the emitted light reaches the photomultiplier.
• the signal amplitude from the photomultiplier is linear with the intensity of the photostimulating light and with the stored photostimulable energy.
• the signal decreases with time.
• the oscilloscope was triggered a second time to measure the offset which was defined as the component of error that was constant and independent of inputs. After subtracting this offset the point at which the signal reaches 1/e of the maximum value was calculated. The integral below the curve was then calculated from the start to this 1/e point.
• the computer multiplies the integral with the sensitivity of the system.
• the sensitivity of the photomultiplier and amplifier have therefore to be measured as a function of anode-cathode voltage of the photomultiplier and the convolution of the emission spectrum of the phosphor, the transmission spectrum of the 6 mm BG 39 SCHOTT (trade name) filter and the wavelength dependence of the response of the photomultiplier have to be calculated. Because the emission light is scattered in all directions only a fraction of the emitted light is detected by the photomultiplier. The position of the panel and photomultiplier are such that 10 % of the total emission was detected by the photomultiplier. After all these corrections have been made a conversion efficiency value (C.E.) was obtained in pJ/mm ⁇ /mR.
• phosphors were prepared in the same way and only the nature and the amount of the activator (dopant) and the nature of the carrier gas were changed.
• the comparative CsBr:Eu phosphors were prepared by adding EU2O3 to the CsBr before firing and the invention CsBr:Eu phosphors were prepared by adding either EuCl2 or EuBr3 to the CsBr before firing.
• CsBr:Tl phosphors were prepared wherein the dopant was either Tl 2 O or one of TlBr or T1C1 3 . 4 H O. All chemicals were used as received from commercial suppliers, except for EuBr and EuOBr.
• EuBr 3 was received in hydrated form from a commercial vendor and dried before preparing the CsBr:Eu phosphors of the present invention. Specifically, hydrated europium bromide was placed in a desicator with desiccant and dried under vacuum for 24 hours. Despite such drying, it is possible that residual water was present and that the europium bromide was in a partially hydrated form. Moreover, given the hygroscopic nature of the materials involved, water may also become included in the europium bromide, in other starting materials and/or in the combined mixture during transfer and handling of such compounds or mixtures. The synthesis of EuOBr is described below.
• Crystals of activated CsBr were prepared by mixing by manual grinding 20 g of 99.999% pure CsBr with the activator compound in the right proportion (see Table 1, below).
• the mixture was placed in an AI2O3 crucible and placed in the quartz tube of a tube furnace.
• the quartz tube was sealed with a flange with water lock and flushed with carrier gas prior to firing and during the firing process.
• the gas flow rate was 120 cc/min.
• the carrier gas was either nitrogen or, alternatively, Ar (with 5.8 mol % H 2 ), and is indicated in Table 1, below for particular examples.
• the furnace temperature was increased from room temperature to 43 °C at a rate of 5 °C/min. Dwell time at this temperature was 6 hours. Next, the temperature was ramped to 700 °C at 10 °C/min. Dwell time at 700 °C was 5 min. The furnace was cooled to room temperature at 10 °C/min.
• the comparative example phosphors were prepared by adding EU2O3 to CsBr. Crystals of activated CsBr were prepared by mixing by manual grinding ca. 20 g of 99.999% pure CsBr with the activator compound in the right proportion. The mixture was placed in an AI2O3 crucible and placed in the quartz tube of a tube furnace. The quartz tube was sealed with a flange with oil lock and flushed with the 5.8 mol % H 2 in Ar carrier gas prior to firing and during the firing process. The gas flow rate was 120 cc/min. The furnace temperature was increased from room temperature to 43 °C at a rate of 5 °C/min. Dwell time at this temperature was 6 hours.
• the temperature was ramped to 700 °C at 10 °C/min. Dwell time at 700 °C was 5 min.
• the furnace was cooled to room temperature at 10 °C/min.
• the crucible containing the phosphor was removed from the furnace, cooled and the phosphor crystals were taken from the crucible. Larger crystalline particles were selected and polished to a thickness of ca. 500 ⁇ m for measurement.
• a film of cesium bromide doped with europium chloride was deposited simultaneously on quartz and silicon substrates.
• the substrate for deposition consisted of a three-inch quartz wafer.
• a three-inch diameter semicircular silicon substrate was attached to one half of the quartz wafer.
• the film of cesium bromide doped with europium was prepared by the thermal evaporation of the phosphor samples in a deposition chamber operating at a pressure of approximately 8 x 10 '6 mbar. Chunks of the bulk phosphor were loaded into three separate evaporation crucibles (alumina) in the chamber.
• the three crucibles were simultaneously heated to 550°C. Deposition was initiated on the substrates facing the crucibles by opening a flag placed between the crucibles and the substrate. The orientation of the evaporation crucibles with respect to the substrate was such that a film of even thickness was deposited over the predefined substrate area.
• the deposition rate from each crucible was approximately 60 A/sec and was monitored using quartz crystal monitors. The distance between the substrate and the evaporation crucibles was 15 inches.
• the quartz and silicon substrates were subsequently removed from the chamber and a protective layer of aluminum oxide (lOOOA) deposited over the film on the substrates using r.f. magnetron sputtering.
• lOOOA aluminum oxide
• the luminescence spectrum was measured from the europium doped cesium bromide film on the silicon substrate using Spex (TRADENAME) double monochromators for the photoexcitation wavelength (280 nm) and to disperse the resulting luminescence which was detected by a spectrally corrected photomultiplier.

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• 2000
  • 2000-06-19 EP EP00942964A patent/EP1203394B1/en not_active Expired - Lifetime
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